Radio system and method for locating enemy artillery



May 31, 1960 c. VAN ATTA 2,939,134

RADIO SYSTEM AND METHOD FOR LOCATING ENEMY ARTILLERY Filed March 4, 19463 Sheets-Sheet 1 A TTOR/VEY A T T R A WM M l ll 1 V 2 R 55523 :2: 105523E G25 lll 18.26 2 53 5 32E 325. L W W B moimuzmw @0255". 105 5002mead... |V|l|l LA? was; mob nooz ALA 452322 1222M; H 2 I: E h E \L d A i6523 .6523 W $24 58 5233 lvlll A 55631 $2.363 A 35:55 4 65:35. w. R v mm kmm y 1, 1960 L. c. VAN ATTA 2,939,134-

RADIO SYSTEM AND METHOD FOR LOCATING ENEMY ARTILLERY Filed March 4, 19463 Sheets-Sheet 2 F|G.2 SETI SET 2 EFFECTIVE AREA OF COVERAGE SHELLTRAJEGTORY F e. 4

/ K LOWER BEAM LOCATER UPPER W ANTENNA )i R g f 0 INVENTOR LESTER C. VANATTA ATTORNEY y 31, 1960 c. VAN ATTA 2,939,134

RADIO SYSTEM AND METHOD FOR LOCATING ENEMY ARTILLERY Filed March 4, 19463 Sheets-Sheet 5 FIG.5

Flefs.

RANGE FROM SET 2 TRAJECTORY INVENTOR Z Q FROM LESTER C. VAN ATTAATTORNEY RADIO SYSTEM AND METHOD FOR LOCATING ENEMY ARTILLERY Lester C.

assignments, to the United States of America as represented by theSecretary of War Filed Mar. 4, 1946, Ser. No. 651,927 7 Claims. Cl.343-13 This invention relates in general to radio object locatingsystems, and, more particularly, to apparatus for determining theposition of mortars from the trajectory of projectiles fired therefrom.

In the course of tactical military operations, one of the most eifectiveand deadly types of enemy action encountered is mortar fire. plicity,and capacity for placing shells behind obstacles suflicient to protectmateriel and personnel against higher velocity projectiles make it ofgreat importance in both offensive and defensive warfare. Accordingly, ameans of defense against enemy mortars may be regarded as of highimportance to ground troops.

Such a means of defense should be highly mobilesince mortars need nofixed emplacements and can be readily dismounted and transported to anew location. Also, the defense means should be capable of being takeninto rough terrain either by motor, or by being carried by a smallnumber of men. A further desirable characteristic is simplicity, so thata minimum operating crew is necessary.

Accordingly, it is one object of my invention to provide a means oflocating the origin of mortar fire.

' Another object is to provide a simple and readily portable'means ofdefense againstmortars.

A further object is to provide a quick andreliable means for locatingthe origin of mortar fire.

In brief, my invention comprises apparatus for electronically observingmortar shells in flight and locating the position of the firing mortarby a process of triangulation. Two antennas, located a predetermineddistance apart, emit beams-of pulse modulated radiant energy whichoverlap above a suspected mortar location. The'beams are thin verticallyand relatively wide horizontally, hence the area of overlap is quitelarge. A

mortar shell rising throughthe beams reflects energy to the antennascausing an indication to appear on a cathode ray oscilloscope in theform of two intersecting lines. Thereflected signal-also causes thebeams to be shifted to a higher angle with the horizontal so that themortar shell again'passes through an overlapping area. The secondcathode ray oscilloscope indication thus obtained, together with theprevious one, enables the range of the mortarfrom each antenna to bedetermined by extrapolation. An accompanying artillery piece is thenemployed to silence the mortar.

The principles and operation of my invention will be more apparent tothose skilled in the art upon reference to the following specifications,claims, and to the drawings in which:

-Fig. 1 is a block diagram of the above-mentioned detector units;

. Fig. 2 is a plan view of the area of overlap between the beams of theantennas shown in Fig. 1;

Fig. 3 is a cross-section through one of the antennas to show itsconstruction;

Van Atta, Winchester, Mass., assignor, by mesne The mortars portability,sim- &@ E

will be small, as is well known to those. skilledgin'the' Fig. 4 is adiagram illustrating the passage of a shell through the beams;

Fig. 5 is a view of a cathode ray oscilloscope screen showing one typeof visual indication which may be employed; and

Fig. 6 is a view of a cathode ray oscilloscope face showing a second andsimpler type of visual indication from which extrapolation may be made.

Each locater unit in the field comprises an antenna mounted on anantenna mast, a radio frequency oscillator which is detachably mountedat the upper end of mast, a truck containing the cathode ray indicator,the

transmitter modulator and communication equipment for contact with otherunits, a cable interconnecting the equipment in the truck and theoscillator, and a generator which may be conveniently powered by a smallgasoline motor to provide a primary source of electrical power for theequipment. The equipment contained in the truck is so constructed thatit may be separated into smaller units, each of which may be transportedon a mans back in terrain unsuitable for vehicular operation. Theantenna and mast may also be made in several sections so that they maybe carried by hand. It will be noted that the installation, due to itscompactness, may be readily camouflaged, the projecting antenna being ofsuch small cross-section as not to be readily discernible to enemyobservers.

The radiated beams, for an illustrative embodiment of the invention inboth upper and lower positions of the beams have a width of 20, asmeasured from the line of direction of maximum energy to the pointswhere the beam power has dropped to half its maximum value. The verticalthickness of the beams is approximately /2 as measured betweenhalf-power points. A normal value of elevation for the beams while'intheir lower position is 1% while in the upper position they are elevated2% above the horizontal.

The area of overlap between the beams is shown in Fig. 2', which is aview of the tern from a point vertically above the beams. It should mateonly and that the area marked effective area oi coverage is notnecessarily limiting, it being possible under certain conditions tosomewhat outside this area.

The shape of the beams is due to the construction of the antennas, eachof which consists of a linear array of dipoles aligned in'a verticalplane and. backed by .a parabolic reflector. A cross-section of one ofthe antennas is shown in Fig. 3, to'which reference is now made,toillustrate this construction. A box girder 20 constructedof a light butformed into a concave parabolic surface to serve as a reflector ofradiant energy. A wave guide 21 carrying oscillatory energy is mountedso as to extend-substantially parallel to the parabolic surface. Alongthe length of wave guide 21 is spaced a plurality of dipole radiators 22which are fed from the wave guide. ,These dipoles may be parallel to theaxisof the girder. Each dipole is mounted on a supporting member 23. Thewave transparent cover 24, which may be conveniently formed of a plasticmaterial, is employed to protect the antenna and parabolic reflectingsurface from damage by weather or physical blows. Sincea number ofdipoles are stacked in the vertical plane, the thickness of the radiatedbeam I art. .The horizontal width of the-,beam,however, is

chiefly dependent upon the physical dimensions of the" parabolicreflector and the position of the linear array with The relative phasesof the'drivingvolt respect thereto.

ages applied to, the dipoles determines the angle of elecombinedradiation patobtain fixes on mortars lying" strong material has oneface' vation of the radiated beam. To effect the switching between lowand high beam positions, the operating frequency of the R.-F. oscillatoris slightly changed. The change in wavelength. of the energy. in thewave guide alters the phaseinwhich' each dipole, mounted in a fixed.

position on.the guide,.is.-fed. To allowLadaptation: of the beamelevationtovarying terrain conditionsit is. possible to incorporate ameans of tuning the oscillator by hand, as well was the automaticswitching. tuning;

Althoughin. one embodimentthe antennas have. had a length of'lS feetexclusive ofthemast, by use .of a construction as described. above thestructurecan withstandfaBO milewind, eventhough the antenna and itssupporting structure. together, weigh .only. approximately 50 pounds.:.

The etiects of Zamortarshelllpassing through the beams can best be.described withre-ference to..Fig; 4. The.- upper andlower. positionsofone of. the. beams are. shown, as. are thelocater antenna and themortar. The

figure has been. exaggerated in certain respects, such as the sizes ofthe antenna and the mortar and theangles of elevation, in ordertoillustrate the operation-more. clearly. When the mortar is fired, theshell describes a path'which is indicated in part by the dotted linelabeled shell trajectory. be substantially parabolic, subject to theefiectsof wind, air resistance, and the like; however, during its'earlyportion, it may be approximated byastraight line without seriousdeviation from-the actual path. This assumption is made in the designandoperation of .the 3 locater apparatus, and it'has-been found thattheerror introduced thereby is negligible. The shell takesqapg proximatelyA -second to pass throughthe'lower beam position, during which time aportion of-the pulsedenergy radiated-from the antenna is reflected fromthe 'metallic substance ofthe shell, and is received atithe-antennafrobe applied to a visual indicating systerrraswillv be describedhereinafter. Reception of .this refie'ctedienergy may also be employedto redirectthebeam' to its. 40

upper position, or a system of alternately, switching the beam up anddown in a regular sequence maybe employed. The former method is.advantageous in that adescending shellfrom a. friendly source'will'register on the visual indicator. only once and;.,therefore,. mayLbe.distinguished from shells emanating fromenemyrposie tions. The timerequired-to switch the beam .to itsiupper position isless thanthat'required for the.-.shell;to;travel1? the additional distance and,therefore,.the:shell: will again reflect energy to the antenna: from. .apoint closer:to the locater. Point Adesignates-theintersectionoflheshell trajectory with the center line ofthe lower beam: sition; point B designates the :intersectionwith'theupper beam position. If azperpendicular is droppedfrom point Bto.the-lower beam. at point C, it can beseen that the difierence inrangemeasurementsbetween theitwo shell positions, as measured from theantenna R, isequal to the distance A-C. The distanceA-C.Xalso representsa difference. in the timeof travelof a radio signal-from R to A. and Band return. Thistimedisparity is retranslated into a.linear'difiereuceonthe cathode-ray tube indicator screen bymeanssimilar; toth'oseemployed in other radio objectlocatingsystems-which include such} visual indication. Examination: of;the; triangles BCA' and. ADM, and ,consideration uof; their geometry,"will.

show that for anglesof elevation: of the order of{2,. hypotenuses AB andAM are'substantially equal, hence AC will be approximatelythe samelength as MD. This: fact facilitatesxextrapolationfrom the known"shell-.positions tothe unknown mortar location. 7

'One ;type of cathode ray tube display-which may be utilized is;showniin Fig.. 5. In this type"ofi'presentation, the. electron beam withinthetubehastwo'resting places; each corresponding; to the location of'one ofthe transmitting; andireceivingc antennas as =inclicated by the Vlegends "Set 1" and Set 2." V v V 'erate either simultaneously oralternately, 1n the latter As is;well known,.this trajectory will 25 Thetransmitters may 0p-.

case switching being performed 30 to 60 times per sec ond. Since, byusing a single indicator located at one of the transmitting stations,one man may make the necessary observations and extrapolations, it isnecessary to connect the sets by a cable over which echo signals are.sent'from the set' withoutan indicator-tothe indicator position. When apulse signal is transmitted from Set 1, the .electron beam ismovcdradially outward in the direction ofth'e radiated beam from theappropriate resting position, marked Set.-.1-, bya suitable linear rangesweep deflectingvoltage. The beam normally makes no illuminated traceonthe face'of' the tube since the 5 control grid of the, tube isheldslightly below cut-off potential. An echo indication, in the form of apositivegoing voltage pulse, is applied to the control grid and causes avisible trace to.appear.on thescreen otthe-tube when the sweep voltage.has displaced the spotirom its resting position a distance.proportional. to .-the range of the target. If the sets arebeingusedalternately. for ,4, second, and the transmittedsignalismodulated at a rate of.6000. pulses per second, these beingnormalvalues,

consecutiveindications will be receivedfromeach set. These will bespreadout. onan -arcbyother' deflecting voltages which rotate. thesweepv through: 293 about the position ofSet '1. duringthis period.Next, the echosignal. from the second setwill be used to modm, latethebeam, the sweeps centering on theposition. of. Set 2 and beingrotated about thispoint by a fourth set of deflecting voltages. "Sincethe mortarshell will remain in the beam at least second,.the arcs abouteach; set will.- be traced at leasttwice. The-intersection A of. thesetwo arcs. locates theshell in range. as it passes. through the lowerbeam. When the: shell passes through, the upper. beam. a. similar. pairof arcsdefinesasecond positionB of. the shell. It can be seen that-theproajection of the'shells trajectory'may be represented byza: linethrough the, two; points 'of intersection, which. line also contains.the mortar. locatiom As was show-n.v in; connection. with. Fig. 4, the:rangediflerenee; between the two points of intersection. will c1ose ly;approximate: the range distancebetween-the first point; of intersectionand the mortar, hence the mortar location'canzeasily'be' obtained byextrapolation .of the trajectory line .toaapoint M an. appropriatedistance behind. the first intersection-z point. V

Whilethis type, of visual presentationmiuimizlesrdise tortion .in thegraphical representation; thevgeneratiom of; proper deflecting voltagespresents; .considerablenifiiculm; in view ofthe fact that: the base lineis :not .fi'xedinle'ngthi; and is subject to tacticalrand terrainlimitations. ,'There.-.- fore,..a presentatiominCartesian coordinates,rather :tharr polar, coordinates, has been found-morenseful. While."

this type of indicationmaynot be, as. accurate'as. the :fore-a 7 0 movedtoward the right along the abscissaofjthe co= ordinates :by asawtooth'voltage applie'd to theuhorizontal. deflecting'plates;Nogvisibledr'acei is as yet prjoducedll Upon reception ofan-echo signal,the controbgridofl the cathode ray tube is raised above cutoff" anda"vertical" trace. voltage is 2 applied" to *theWertical deflectingplates to produce a..visible, straight, vertical trace, The beam" thenreturns to. pointO, and a similar: procedure" ierculowed to produce ahorizontal trace from an ech'o sig nal. from Set 2;. In,like fashion, asecond intersection point is obtained from the high beam position-,:.andextra= polation. is. carried; out; as described.hereinaboveitofdetermine the range of the mortar origination:point-fromthe transmitters. Whenthe: range. of.--the.-mortar b'othtransmitters is known, the geographical tpgsitiou'rot-i the mortar canreadily be determined by use of a compass on an artillery map. Incarrying out this construction change the points in the map from whichmeasurements are made. I

The system may also be used, particularly if continuous switchingbetween high and low beams is employed, to spot friendly counter fireagainst the mortar position. Hence, corrections to poorly aimed counterfire may be given the artillery commander quickly and accurately.

The complete system is illustrated in block diagram in Fig. 1. and Set2, respectively, both of the units being interconnected by means of acable indicated by the dotted lines. Since both sets are similar, exceptfor certain components which are common to both, only Set 1 need bedescribed in detail, it being understood that the components of Set 2indicated by the primed reference numerals, are identical in structureand function to the components indicated by the same, but unprimed,reference numerals of Set 1.

Set 1 includes an antenna 5 comprising a vertical dipole array andreflector 20. A wave guide 21 connects the dipoles to a transmittingoscillator 7 which is re-' petitively pulsed by a modulator 11 which isrepetitively energized by a switch unit 16, which is a generator ofspaced pulses of suitable repetition rate and duration. A frequencycontrol means 17 is coupled to oscillator to periodically shift thefrequency of the oscillator thereby to shift the lobe of the antennapattern.

The echoes picked up by antennas 5 and 5' are applied to receivers 12and 12, and the outputs of both receivers are applied to the intensitygrid of an oscilloscope 15. The output of vertical trace generator 14 isapplied to the vertical deflecting plates of the oscilloscope, and theoutput of horizontal trace generator 14' is applied to the horizontaltrace generator. When an echo is received on Set 1, the grid of theoscilloscope is raised above cutoff, and the voltage from generator 14produces a straight line vertical trace. Similarly, a horizontal traceis produced by generator 14 when an echo is received by Set 2.

The pulses in the outputs of modulators 11 and 11' are applied to rangesweep generators 13 and 13, respectively. The output of generator 13 isapplied to the horizontal deflecting plates of the oscilloscope, and theontput of generator 13' is applied to the vertical deflecting p ates.

The outputs of receivers 12 and 12' are applied to frequency controls 17and 17' when two position switches 18 and 18' are in the upper positionas shown, so that the antenna lobes are shifted when the first echo isreceived. When the switches are in the lower position both frequencycontrols are periodically operated under the control of switch unit 16so that the antenna lobes are periodically shifted up and down.

The system described provides sufficient accuracy in performance with anabsoluteminimum of equipment. It is possible to accomplish spotting ofshells with object locating systems using an antenna which is moved toscan a given area. However, the bulk and weight of the scanning andsynchronization apparatus is such as seriously to reduce the mobility ofthe set.

While there has been described hereinabove what is at present consideredto be a preferred embodiment of the present invention, it will beobvious to those skilled in the art that changes and modifications maybe made therein without departing from the inventive concept.

What is claimed is:

1. Apparatus for determining the location of an artillery piece firing aprojectile comprising a first radiator of electromagnetic energy, firstmeans for generating The two spaced units are indicated as Set 1'radiator, the radiated energy being in the shape of a beam verticallythin and'horizontally thick, second energygenerating means and a secondradiator spaced apart from said first generating means and radiator byapredetermined distance and having characteristics substan tially similarto said first generating means and radiator, means for directing thebeams of energy from said firstv and second radiators through a givenregion over the artillery location, meanscoupled to said radiators foraltering the'angle of elevation of both beams simul-v taneously by asimilar amount, means associated with each of said radiators forreceiving energy reflected from the projectile originating at saidartillery piece and passing through the beams at two difierent angles ofelevation of each of said beams, and means comprising a single indicatoroperatively connected to both of said receiving means for determiningthe range of the projectile for each angle of elevation of said beams.

2. Apparatus in accordance with claim '1 wherein there is provided inaddition means coupled to said radiators and receiving means foraltering the angle of elevation of the beams in response to an echosignal.

3. Apparatus in accordance with claim 1 wherein in addition said meansfor determining the range of the projectile includes cathode ray tubemeans.

4. Apparatus for determining the location of an artillery piececomprising a first radiator of a beam of electromagnetic energy, firstgenerator means for generating oscillatory energy and supplying saidenergy to said first radiator, second generator means and a secondradiator similar to said first generator means and radiator spaced apartfrom said first generator means and radiator by a predetermineddistance, means for directing the radiated beams of energy from saidradiators through a given region over the location of the artillerypiece, means coupled to said radiators for increasing the angle ofelevation of both beams within a time less than that required for aprojectile from said artillery piece to pass from the position of thebeams at their lower elevation to the position of the beams at theirhigher elevation means associated with each of said radiators forreceiving energy reflected, from a projectile originating at saidartillery piece and passing through the beams at their two differentangles of elevation, and means comprising a single cathode ray tube forindicating reflected energy received on both radiators for determiningthe higher angle of elevation within a time less than that.

required for the projectile to pass from the lower to the higherpositions of said beams so that the projectile will again pass throughthe beams to produce a second set of reflections, applying voltagesdeveloped from said first and second sets of reflections to a cathoderay tube so that each set of reflections make visible a pair ofintersecting lines on the screen of said tube, the points ofintersection of said lines being spaced apart from two reference markson the face of the tube a distance substantially proportional totheranges from the two stations to the projectile, and extrapolating on astraight line joining the two points of intersection a distancesubstantially equal to the ratio between the two angles of elevationtimes the distance between the intersection points to find the rangesfrom each station to the origin of the projectile.

v6.1 Themethod; of locating; the point1of;.origin;,;of:a,projectile.comprising. the; steps;,.0f radiating: broad; flat' beams :ofpulse-modulated: radio: signals at a very low anglev of elevation: fromtwo physically distant stations into substantially the same space.- inarregion over the.

poinbof. origin. of theprojectile, receiving. at each re diating.station .echo signals..reilected from .the projectile.

rising throughtheoverlappingbeams; elevating the: beams simultaneously,to twice saidlowangle .of elevationwithin-a timeless than that requiredfor theprbiectilezto. passzfromthe-lower; to thewliigherpositionstofsaid beams so that: thenprojectile will againi'passthroughtthe beams toproduce a second set of "reflections, depicting the. range of" eachradiating: station :from thezlprojectile: at each of itspassages:"throughzthe beams,. plotting, said intersection points.graphicallyv in: relation to:.-the' .location-.of said transmitters,and: extrapolating; on-'.a straight line i joining the. two points:ofintersectionzaadistance. substantially equal to the distancerbetweentheezintersectionapoints to. find itheranges. from: eachstation"tostheorigin of the projectile. V I

7.. The method: ofzlocating.the.point:.of origin of an objectdescribing; a. trajectoryrin spacer comprising the.-

steps; lof radiating broad, flatbeamS .of.i-'pulse-modulatedradio-signals at-avery low'angle ofelevation from a'pair.

of physically. separated.stationsrinto substantially the same; space inazregion. near: said. origim. receiving; ataeach radiating: station;echo signals reflected; from the; object. p 'i roughr h v flapPi a eams;appr at ly,

doubling thle; angle, of; elevation/of the. beams. within;- a:

time less thanthat required for-theprojectile;tqpass from; the lowertojthe higher positions ofsaidbeams so, that theobject; will again, passthrough the beams to produce at least one additional set of reflections,applying volt ages developed, from said sets ofreflections to a'cathoderay tube, causingeacl' set of' reflections to make visible; onthe screenof said tube ay-pair of lines intersecting at a point spaced fromreferencemarks onvthe face of the tube by distances substantiallyproportional to the ranges from therstations. to the moving object, andextropolating on a.straight. line-joiningythe points of intersection a;distance substantially-equal to the dlStQHCQbfitWfifiIljCQfl-g secutive'intersection points to find the rangesfromeach station; to the originofthe object.

References Cited inthe. file. of lthisfpatent

